NOTE: The article mentions pics. The pics were lost during a hosting move. We since replaced the pics with the first part of the rebuild video for the 3G. You get the rest of the video links after purchase of the kit.
3g Rebuild Video First, let’s start out with the physical identification and attributes of the 3g series alternator. The 3g, or third generation, is a family of alternators for Ford. (PIC 40)There are various mounting configurations and pulley sizes (show 7791,7750,7771)but the internal structure and parts are basically the same. Like all other alternators the shell is aluminum, separated by the stator laminations in the middle. We refer to the 3g as in all other alternators as rotor, rectifier stator ass’y (which contains diodes) rear plate, voltage regulator, through bolts,pulley and nut, and front plate ass’y.
pic 54All 3g’s have the 6 ribs in the front plate, behind the pulley, arranged in pairs, giving the appearance of spokes on a rim. Inside each set of spokes is either 2 holes or 4. This is the easiest way to tell if you have a 130 amp large frame 3g, or 95 amp small frame 3g. The 4 holes is the smaller frame diameter, 2 holes is the larger frame diameter. (PIC 41) This is the voltage regulator brush holder ass’y.(PIC43) Take the t20 torx tool and remove the 4 screws.
Remove the regulator by raising it up towards the outer diameter first, then slowly pull out, using care not to lose the 2 brush springs. (PIC 44) The most common failure on a 3g is the bottom brush burns a groove in the commutator (actually called a collector ring or slip ring). This happens to over 90% of the alternators that reach 100-120K miles. This scenario would be similarly compared to brake pads wearing through the rotors.(PIC52) Inspect the brushes for signs of oil, antifreeze, or bad spring tension. Look inside where the brushes ride. With the alternator sitting on the pulley, the groove on the bottom will be the deepest. With a flashlight inspect the groove.
If the groove on the bottom is a darker color, or more burnt looking than the top one, you have just discovered, for sure, you have a bad alternator. Disregard all other previous spin testing or “know it alls”.
If you’re having a dead battery or periodic idiot light problem…. you’re on the right track, so keep going. If you don’t find burn marks on the slip ring, you may want to reload the voltage regulator with a paper clip, and take the alternator to a part store to have it spin checked. You’ll be looking for bad diodes or a blown voltage regulator. Before going any further, take this opportunity to inspect the outer case of the alternator. Sometimes the outer cases on alternators will have a crack. PIC 46 Alternators can even be “locked up” which means the pulley won’t spin. This almost always makes the core no good. The unit has been subjected to too much age and rust corrosion. This makes a successful rebuild extremely difficult, even for veteran rebuilders. Cracks usually occur more often on vehicles, like Cougar or Mystique, that have the alternator located close to the road, where it picks up moisture on rainy days. Also vehicles that have been parked for extended periods tend to have cracks in the aluminum more often. If you can see cracks before you even get started, this is a good time to get another core. Go to car-parts.com and call a junk yard near you or have one shipped. Don’t be scared by the high prices at the top of the page if you view them in cost $ order. Start somewhere in the middle and work your way towards the “call” entries. The first step for further dis-assembly is to mark with a center punch or a chisel the front and rear plate so alignment can be restored upon re-ass’y. PIC 46Remove the 3 thru bolts with a 5/16 socket or 8mm.
If the bolts are corroded apply penetrate oil and wait 5 minutes. Gently tap the drive end housing where the threads are located. For occasional extreme cases, heat may be necessary. Holding the front with one hand, hammer off the rear housing by tapping and rotating.PIC 47 Remove the pulley with a ½ inch impact and a 15/16 socket. PIC 42You can hold the pulley with your hand if you put a rag around the pulley. If you don’t have air tools, place a t50 torx in a vise, and support the alternator with the help of another person. Then, use a 15/16 wrench and tap it CCW with your hammer.
The easiest way to remove the pulley from the shaft is with 2 big screwdrivers placed 180 degrees apart between the drive end housing and the pulley. The trick is: don’t pry with them, twist with them simultaneously. Sometimes a little heat will help immensely. Pulleys rarely corrode to the shaft because the metallurgy is similar, but for very rusty situations, some penetrating oil or a puller may be necessary. Never, ever tap or pound on the shaft while holding the pulley. After removing the pulley, polish the shaft with scotch brite or 400 grit cloth and put some penetrating oil around the bearing.
If your wife’s not home, bake the alternator at 400F degrees for 20 min. You can also use a propane torch, but you have to distribute the heat evenly, and avoid too much heat going in to the windings. This will take about 10 minutes to expand the aluminum enough to break the corrosion and allow further dis-assembly. The following is for right handed, left handed would be the opposite. You need an oven mitt or several rags for your left hand, while pounding with the ball peen hammer with your right. Working quickly, before too much cooling time passes, place the alternator on it’s side on a metal bench top, concrete floor or hard surface. Smack with hammer for 2-3 minutes around total circumference. During this step, it’s a good thing to see the metal stator laminations start to appear out of the aluminum drive end housing.
You have to hit pretty hard, but don’t smash the aluminum. If you do crack it, you can order a new one, and the price is pretty reasonable, but everybody hates delays. After this step, start holding the rectifier stator ass’y with your left hand while pounding on the drive end housing laterally with the ball peen. You must hit in 180 degree increments. For ford trucks with 4.6/5.4 L there’s no aluminum ear on the one side to tap on. Take one of the thru bolts and screw it in to the top. Then you can use that to tap on. Don’t worry, we’ll include a new bolt in the kit in case the old one gets bent.PIC 49 The drive end housing should be off the shaft, if the bearing is stuck to the shaft, here’s what to do.
Place the assembly upside down in a vise. Leave 1/16 inch clearance on both sides of the jaws. Thread the nut onto the shaft so 1 thread is still visible from the top. Spray penetrating oil on the bearing inner race and wait 5 min. Get a wood block, pound the block placed on top of the shaft until the joint breaks loose. If that doesn’t work, Heat the bearing/shaft area with a propane torch for 5 min. Get a wood block, pound the block placed on top of the shaft until the joint breaks loose. pic 51 Remove the 3 bearing retainer bolts in the drive end housing with the 5/16 socket.
pic55Turn the frame upside down and pound out the bearing with the help of a 3/8 extension. Pound from different locations around the inside race of the bearing to help break it loose. pic57Spray out with electrical cleaner. Apply a thin layer of red loctite to the aluminum hole. Tap in bearing with help of 3/8 extension. Only tap on the outer race.
The trick is to get it pushed in perfectly straight, and tap only on the outer race. Keep watching from side view, it’s the easiest way to visualize where the bearing needs tapped to keep it straight. You can see the bearing’s a little higher in this area right here so that’s where it gets lightly tapped. Then, when the bearing is completely in, install the cover and the three retainer bolts. Alternate bearing installation method is heat the aluminum with a propane torch for 3 minutes in the area where the bearing goes.
Apply red loctite to the bearing, drop it in. Install cover and bolts. If you break a bearing cover bolt, one will suffice, if you use plenty of red loctite and modify the retainer with a hacksaw as shown. As added insurance, stake the aluminum with a chisel so that some of the aluminum housing is smashed over to retain outer race. If you prefer: new plates can be ordered. Clean the rectifier/ stator winding ass’y with electric motor cleaner. Scrub the solder joints with a wire toothbrush. Inspect the rectifier solder joints with a magnifying glass. This is a solder joint that has been burnt. There is arcing or burnt marks around the diameter of the diode stem. This is what a single diode looks like.
pic 60This is the body pic 62, this is the stem.pic 61 If there is arcing on the surface area of the stem where it solders into the rectifier, it can be repaired. If there are signs of heat on the top of the diode body, the rectifier is not repairable. Inspect all the diodes in the rectifier for warping or bubbles on the surface of the diode itself. If any diodes are bubbled or warped, the rectifier is junk. Rectifier problems are rare in the 3g under normal circumstances. Bad diodes probably would have been caused by cross polarity (someone jumped the car backwards, or just a horribly bad battery).
New rectifiers can be ordered reasonably. The solder joints should have no cracks or burn marks particularly where the stator wires come up through. The joint that has the most stress from dis-assembly is the first one on the left. Any little cracks or burn marks must be re-soldered. Clean the solder area first with a clean (new) wire tooth brush. See the free video on soldering. Use the soldering gun to re solder any diode stem burns or damaged stator leads now.pic 64 & 65 .This a good time to do cosmetic work if desired to the ferrous portions of the stator windings. You can use a stationary buffing wheel or an orbital buffing wheel that fits on your electric drill. Be careful to stay away from the windings on the inside of the stator.
You don’t have to get all the rust, but get as much as you have the patience to. Also sand paper the ground path on the rectifier and the drive end housing. Place a thin layer of white lithium grease on the areas just sanded to prevent future corrosion. Inspect the stator laminations for disfigurement due to rusting. This usually occurs in units that are in extremely rusty condition. When you order a new stator, it comes with a new rectifier already soldered to it. If you want to, you can spray paint or ignition sealer the metal stator laminations, and the top of the rectifier.
Now, to remove the rear bearing, use penetrating oil on the inner race of the bearing. Wait 5 min. Place the rotor in a vise. Use a 1/4×6” extension and ball peen hammer to tap off the bearing.pic 66 If necessary, use heat and hit it as hard as you need to, to break the inner race off the shaft. If you have a bearing splitter you can use that, if you have a 2 jaw puller, you can use that. If the bearing breaks, as is possible in some really stubborn cases, remove all the shrapnel down to the inner race. Grind a flat side through the inner race till you can see the shaft. If you grind a little bit of the shaft, it won‘t hurt anything, but try to keep it at a minimum.
This does 2 things, it heats up the race which expands it, and it breaks the bond somewhat so that the race can be easily tapped off with a hammer and chisel after placing the rotor in a vise. Now is the time to replace the slip ring on the rotor. Cut the leads coming up from the coil 1/8” away from the factory spot weld between the slip ring and the spot welds with ordinary wire pliers.pic 68 & 69 Place the rotor in the vise. Drive the 2 big screwdrivers between the plastic on the slip ring and the metal base on the rotor, 90 degrees away from the spot welds, and 180 degrees apart from each other.
pic 70 Use the screwdrivers to pry up on the slip ring until it comes off the shaft. pic 71Wipe off the shaft, apply a thin layer of oil on the shaft. Use a 3/4 socket to tap the new slip ring down into position on the rotor. USE EXTREME CAUTION : The plastic on the slip ring is extremely brittle. Stop tapping the slip ring 1/32” before the bottom of the slip ring contacts the base. USE EXTREME CAUTION : The two 180 degree apart feet of the plastic are the bottom of the slip ring. THIS is the part that must stop 1/32” before contacting the metal base. The most delicate part of the operation is to insure perfect alignment of the 2 white plastic feet on the slip ring to be aligned with the open spots on the rotor.
pic 74 Don’t be concerned at this point with the copper leads lining up with the spot welds. Focus on the over view to exactly align the white plastic feet with the openings on the rotor BEFORE you start to tap on the slip ring.pic 75 Make a couple taps, with a ¾ socket and hammer. Stop and double check alignment.pic 73 Then continue tapping with extreme caution to stop 1/32” from bottoming out, because the slip ring will crack very easily. Any cracks, even hairline cracks, will severely jeopardize the integrity of the rotor because severe centrifugal forces work on the slip ring. Now clean both the copper straps and both spot weld sections with the metal toothbrush.
pic 72.Carefully clean the spot welds so as not to break the plastic supports that come up from the coil. Broken plastic supports look like this. In tact ones have little play like this. Broken plastic supports will jeopardize the integrity of the rotor as it spins at super high speeds because of centrifugal force. Wrap leads around spot welds with needle nose.pic 77 & 78 Apply flux. Heat. Fill the pocket without allowing drips to form on the bottom.
Try to get solder to flow along seam where copper lead comes in contact with itself.pic 80 Inspect solder, that there should be no drips, or solder that dried near the metal surface. Test rotor with digital volt meter(DVM) set on 100k ohms. You should read continuity from ring to ring, then open from either ring to the shaft (ground). Once again inspect solder joints to insure that no solder is near body of rotor as this would have bad consequences. Now you can install the rear bearing. Use a drop of red loctite and tap the bearing on the shaft with a 3/8” socket. See the free video on selecting the right bearing tool.
This will help you select a socket from your tool box that goes over the shaft, but doesn’t damage the bearing. Lightly sand to remove corrosion the inside of the drive end housing. Polish the drive end of the shaft with 400 grit sand paper or scotch brite. Place the drive end plate face up in the vice. Put a thin coat of red loctite on the shaft where the bearing will ride. Place the shaft in the bearing, if it gets stuck, tap it in with a piece of wood or the hammer handle. Install the pulley. Install provided lock washer and nut, tighten nut using opposite method of removal. ½ inch electric or air impact).pic 88 Hold the plate in one hand and spin the pulley to make sure nothing clicks or hits.
Dip a finger in lithium grease and coat the inside of the aluminum drive end plate to help prevent future corrosion. Flip the rear plate over and sand the ground path circumference. Place a light coating of lithium grease on this area. Align the rear plate on the rectifier ass’y and place it over the upturned rotor noting the alignment marks that we placed on the aluminum frames before dis-assembly.pic 81 Tap the stator and rear plate down onto the drive end ass’y by tapping around the diameter of the rear plate.
pic 82If it hits a stopping point, observe the parallel of the rectifier bottom to the top of the drive end housing and tap harder at the widest point. Also note the center of the rear plate where it must be tapped onto the bearing. As you near completion, buff the bolts, especially underneath the heads of the bolts. Place lithium grease on the bolts and you can use them if necessary to draw the 2 pieces together. pic 83When the bolts tighten, start trying to spin the alternator. Don’t worry, being stuck is common. Tighten the alternator pulley nut in the vise. Briskly tap the sides of the alternator and the top of the alternator while turning with your hands, the alternator itself.
A trial and error method can be used for the sequence of tightening or loosening the bolts while spinning and tapping. After the alternator can be held in your hand and spun with only minor resistance, lay the alternator on its side. Where it feels like it has a spot, hit the side of the alternator, then snug up the bolts a little. pic 84 As long as all the major resistance is gone, the car will remove anything else after it runs for a little while. Now we’re ready for the final step: installing the regulator ass’y. Wire tooth brush the aluminum where the regulator mounts. Install a thin layer of lithium grease.
Place the regulator in the slot, pic 85install the 4 t20 torx heads. Pull the brush pin. pic 86 ASSEMBLY COMPLETE ! If the alternator is labor intensive to re-install, you may want to take it to a local part store for a spin check. Some of the people at the store may not know how to check the alternator so you may be able to assist them by making sure they have voltages at all the proper places. Just like on the car, A on the regulator is battery voltage, I is hot through the idiot light, but doesn’t have to be a full 12VDC. The single terminal that is off by itself is connected to the middle terminal of the voltage regulator.
This has nothing to do with charging procedure, but it causes the idiot light to come on if it’s unplugged. Some unscrupulous spin machines have extremely high standards that must be met in order to pass the alternator. It’s great for sales. Don’t fall for it. All you need is amps, volts, light out and no shorted phase. First look at the volts. If the volts go to at least 14VDC but not over 15VDC: that’s good enough. The amperage output can only be tested under load. So when the simulated load is applied, only the amp meter is observed, and the voltage is ignored. The 95amp goes to a minimum of 90ADC if they’re spinning it fast enough. The 130amp must achieve a minimum of 125ADC if they’re spinning it fast enough.
Different machines across the nation will have different methods of detecting shorted phase. That means the alternator has either a bad or open diode, or a bad stator winding. Most alternators will charge at a little less voltage and a little less amperage than they should, but how much less causes confusion. The alternator will howl and get louder as the load increases. Also there will be an unusual amount of heat. Remember don’t fall for the “Your alternator is .2 volts too low”, or “Your alternator needs to be 7 more amps” If you have 14VDC, relatively close to the amount of amps when loaded, idiot light out, and no shorted phases, everything will be just fine.
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